The invention relates to a device and a process for excavating and back-filling of soil, in particular for laying of pipes in ditches.
When ditches are excavated, in particular for the purpose of laying pipes, excavators are used which comprise a pivoted excavator bucket at the end of a boom. The boom is made up of a plurality of boom arms connected to each other with hinges, which allow a given movement of the excavator bucket controlled by an operator or a control unit. The ditches in which the pipes are laid are approximately 3 m deep and approximately 1.20 m wide.
During conventional laying of pipes first the ditch is dug and the excavated material transported to a dump site. Then a supporting layer for the pipes is prepared in the soil and the pipes are embedded up to at least half their diameter in a grit or gravel layer.
Filler capable of being packed is supplied, fed into the ditch and packed. The ditch is then filled with crushed stone and covered with asphalt, if necessary.
This procedure presents several drawbacks. Removal of the excavated soil and dumping of the excavated material on a dump site involves costs of approximately DM 40/m3. From the ecological point of view dumping of the soil is unnecessary. Further costs arise for the filler supplied. Furthermore, removal and delivery of the materials by truck require thorough logistic planning. The site must be cordoned-off to a large extent to control the truck traffic so that it is not possible to set up a small mobile site. Finally progress of work depends to a large extent on the traffic and that the waste is continuously removed in due time and the filler is continuously delivered in due time.
It is the object of the invention to provide a device and a process for excavating and backfilling of soil, which allow a more rapid progress of work with simultaneous saving of base material and reduction of waste.
The invention preferably provides for a milling/mixing rotor to be mounted on the excavator bucket. The arrangement of the milling/mixing rotor on the excavator bucket preferably allows different working cycles to be carried out using one and the same site vehicle. First the excavator bucket can be used in a conventional way for excavating and backfilling of soil. With the aid of the milling/mixing rotor the soil can be milled, loosened and comminuted in a separate working cycle so that the excavated soil can be reused.
The volume of the excavator bucket is divided into a receiving chamber for the excavated material and a mixing chamber for the milling/mixing rotor. The mixing chamber surrounds the milling/mixing rotor and is not connected with the receiving chamber of the excavator bucket.
A spray means can spray a liquid binder into the mixing chamber of the excavator bucket.
In this way binder is fed during milling of a layer and mixed with the loosened and comminuted material. The treated material can then be used as filler. The excavator bucket may further comprise a distribution means for powdered binder.
For this purpose the excavator bucket preferably comprises a storage chamber for powdered binder. Said storage chamber may e.g. be arranged in the rear portion of the excavator bucket.
The powdered binder may be distributed from the storage chamber with the aid of a rotary lock preferably arranged behind the milling/mixing rotor. The rotary lock is arranged axially parallel to the milling/mixing rotor.
A control unit may control the travel of the excavator buckets in dependence on the position of the boom arms with the given milling depth being adjusted.
In this way the path of the excavator bucket is kept constant with the milling depth being kept constant, too, without the operator having to carry out complicated steering movements.
The milling/mixing rotor is partially surrounded by a circularly curved covering hood in the excavator bucket with the covering hood defining the mixing chamber in the excavator bucket. The milling/mixing rotor is mounted in the side walls of the excavator bucket laterally defining the covering hood.
The process according to the invention preferably provides for the first ditch section to be excavated in a conventional manner with the excavated material being removed, a supporting layer being prepared and pipes being placed and embedded in a grit and gravel layer in the first ditch section, and for the following ditch section to be first milled in several layers at a given milling depth with the milled material being simultaneously loosened and mixed and binder being added. The material treated this way is excavated and placed as filler onto the pipes located directly upstream. When work is started, a first ditch section is first prepared in a conventional manner for laying of approximately 1 to 3 pipe/pipes and for being backfilled after laying of the pipes. The following ditch section is not excavated by the excavator bucket in a conventional manner but prepared with the aid of a milling/mixing rotor and the milled material is removed layer-wise along a fixed path. During milling, loosening and comminution of the material layer binder is added and admixed to the loosened layer. Only then is the loosened and treated layer excavated with the same excavator bucket in excavating position and placed as filler onto the pipes located directly upstream. When the filler for the pipes in the first ditch section has been completely unloaded, a corresponding second upstream ditch section is cleared into which 1 to 3 pipe/pipes can be placed so that treated soil can be used again as filler during the following working cycle.
The process according to the invention presents the essential advantage that the excavated soil can be used as filler after having been treated and binder having been added, which makes the complete removal of the excavated material and delivery of the required filler superfluous. Costs for dumping and filler as well as for removal of the soil and delivery of the filler are thus saved.
Owing to the fact that transports are not necessary a continuous progress of work is possible so that the working time and the size of the site can be reduced. Finally the traffic to and from the site is considerably reduced either since only the material for the grit, gravel and crushed stone layers must be delivered and small amounts of waste must be removed.
Hereunder an embodiment of the invention is explained in detail with reference to the drawings in which: